U.S. patent number 3,989,904 [Application Number 05/537,066] was granted by the patent office on 1976-11-02 for method and apparatus for setting an aural prosthesis to provide specific auditory deficiency corrections.
This patent grant is currently assigned to John L. Holmes. Invention is credited to Vernon O. Blackledge, John S. Rohrer.
United States Patent |
3,989,904 |
Rohrer , et al. |
November 2, 1976 |
Method and apparatus for setting an aural prosthesis to provide
specific auditory deficiency corrections
Abstract
Apparatus for setting or adjusting an aural prosthesis, such as
a hearing aid, in order to provide compensatory amplification or
attenuation for aurally handicapped persons such that the
prosthesis compensates for the specific auditory deficiencies of
that person. The apparatus includes a master hearing aid having one
or more adjustable gain controls for determining the person's
preferred word discrimination levels for a plurality of frequency
bands. As the master hearing aid is set at the person's preferred
level for each separate band, a reciprocal control coupled to each
master control is adjusted at the same time. A hearing aid is then
selected having an acuity deficiency correction characteristic
generally similar to that determined by the previous test
information, and that hearing aid is coupled to the reciprocal gain
controls. The hearing aid selected is of a type which may have one
or more adjustable filter networks and a maximum power output
adjustment or any combination of one or more of these. Whatever
adjustable controls the hearing aid may have for its filters or for
maximum power output are then adjusted by reference to the
reciprocal gain values so that the audio response curve of the
hearing aid closely approximates that of the master hearing
aid.
Inventors: |
Rohrer; John S. (Tempe, AZ),
Blackledge; Vernon O. (Scottsdale, AZ) |
Assignee: |
Holmes; John L. (Scottsdale,
AZ)
|
Family
ID: |
24141052 |
Appl.
No.: |
05/537,066 |
Filed: |
December 30, 1974 |
Current U.S.
Class: |
381/320 |
Current CPC
Class: |
A61B
5/121 (20130101); H03G 3/04 (20130101); H03G
5/025 (20130101); H04R 25/502 (20130101); H04R
25/356 (20130101) |
Current International
Class: |
A61B
5/12 (20060101); H03G 3/04 (20060101); H03G
5/02 (20060101); H04R 25/00 (20060101); H03G
5/00 (20060101); H04R 001/22 (); H04R 025/00 () |
Field of
Search: |
;179/17R,17FD,1A,1D,1N
;128/2Z |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Stellar; George G.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is directed to inventive concepts which are
related to those described in U.S. Pat. No. 3,784,745, issued Jan.
8, 1974, entitled "Method and Apparatus for Providing Electronic
Sound Clarification for Aurally Handicapped Persons"; U.S. Pat. No.
3,784,750, issued Jan. 8, 1974, entitled "Apparatus and Prosthetic
Device for Providing Electronic Correction of Auditory Deficiencies
for Aurally Handicapped Persons"; U.S. Pat. No. 3,818,149, issued
June 18, 1974, entitled "Prosthetic Device for Providing
corrections of Auditory Deficiencies in Aurally Handicapped
Persons"; and application Ser. No. 350,377, filed Apr. 12, 1973, in
the names of William P. Stearns and Barry S. Elpern, entitled
"Method of Fitting a Prosthetic Device for Providing Corrections of
Auditory Deficiencies in Aurally Handicapped Persons", now U.S.
Pat. No. 3,848,091 dated Nov. 12, 1974. All of the above-cited
patents are assigned to the assignee of the present invention, and
the disclosures thereof are incorporated herein by reference.
Claims
We claim:
1. Apparatus for adjusting an auditory prosthesis of the type
having control means for controlling the volume thereof over at
least part of the audible band, comprising:
measuring means for establishing a person's auditory requirement
over said part of the audible band, said measuring means including
first gain control for controlling the gain of said measuring means
over at least said part of the audible band, adjusting means
responsively coupled to said first control means for adjusting the
gain of said measuring means;
second gain control means having variable means for adjusting the
gain thereof, the adjusting means of said second control means
being responsively coupled to the adjusting means of said first
control means such that the gain of said second control means is
always the reciprocal of the gain of the corresponding first
control means; and
input means for introducing audio frequency signals to said
prosthesis, output means for receiving audio frequency signals from
said prothesis, said second gain control means being electrically
coupled to said output means, an indicating means, and means for
coupling said second control means to said indicating means.
2. Apparatus for setting specific auditory corrections into an
aural prosthesis of the type having an amplifier and an adjustable
gain control for said amplifier, the combination comprising:
measuring means for establishing a person's audio discrimination
capability within the audio frequency spectrum, said measuring
means including first gain control means for controlling the gain
of said measuring means, and means for adjusting said control
means;
second gain control means having variable means for adjusting the
gain thereof, the adjusting means of said second control means
being responsively coupled to the adjusting means of said first
control means such that the gain of said second control means is
always the reciprocal of the gain of the corresponding first
control means; and
input means for introducing audio frequency signals to said
prosthesis, output means for receiving audio frequency signals from
said prosthesis, said second gain control means electrically
coupled to said output means, an indicator means, and means for
coupling said second control means to said indicator means.
3. Apparatus for setting specific auditory deficiency corrections
into an aural prosthesis of the type having a filter means
providing an audio pass band and an adjustable gain control for
said pass band, the combination comprising:
means for establishing a person's audio discrimination capability
within said pass band of the audio frequency spectrum, said
measuring means including first gain control means for controlling
the gain of said pass band, and means for adjusting the gain of
said first control means;
second gain control means having variable means for adjusting the
gain thereof, the adjusting means of said second control means
being respectively coupled to the adjusting means of said first
control means such that the gain of said second control means is
always the reciprocal of the gain of the corresponding first
control means; and
input means for introducing audio frequency signals to said
prosthesis, output means for receiving audio frequency signals from
said prosthesis, said second gain control means electrically
coupled to said output means, and indicator means, and means for
coupling said second control means to said indicator means.
4. Apparatus for setting specific auditory deficiency corrections
in an aural prosthesis of the type having a plurality of filter
means providing audio pass bands and adjustable gain controls for
each pass band, the combination comprising:
means receiving complex phonic input signals, filter means dividing
said input signals into a plurality of discrete pass bands, first
adjustable gain control means coupled to each of said filter means
for adjusting the gain within each pass band;
second adjustable gain control means coupled to each of said first
gain control means to form a pair, each pair of control means being
simultaneously adjustable such that the gain of said second control
means is always the reciprocal of the gain of said first control
means; and
means for introducing input signals to said prosthesis, said input
signals corresponding in number to the number of filter means of
said prosthesis and each having a characteristic audio frequency
within one of the pass bands of said prosthesis, output means for
receiving output signals from said prosthesis, said second gain
control means being coupled to said output means, an indicator
means, and selector means for selectively coupling said second gain
control means to said indicator means.
5. Apparatus for setting specific auditory deficiency corrections
in an aural prosthesis of the type having a plurality of filter
means providing adjacent audio pass bands and adjustable gain
controls for each pass band, the combination comprising:
means for establishing a patient's audio discrimination preferences
within discrete pass bands of the audio frequency spectrum, said
means including a plurality of filter means establishing said pass
bands, first and second gain control means associated with each
filter means, each of said first gain control means being
operatively coupled to each filter means to control the gain in
each pass band;
each said first and second gain control means further including
adjusting means, the adjusting means of said first control means
being operative to set the gain in each pass band for preferable
aural discrimination, the adjusting means of each second control
means responsive to the adjusting means of one of the first control
means to always provide a gain which is the reciprocal of the gain
of the first control means; and
input means for selectively introducing audio frequency signals to
said prosthesis, output means for receiving audio frequency signals
from said prosthesis, said second gain control means electrically
coupled to said output means, an indicator means, and selector
means for selectively coupling said second control means to said
indicator means.
6. Apparatus of the type described in claim 4 wherein said aural
prosthesis includes two filter means each providing a band, the
band of one of said filters being substantially completely included
in the band of the other of said filters.
7. Apparatus of the type described in claim 1 wherein the input
means to the prosthesis includes a series coupled variable
calibrating resistor.
8. Apparatus of the type described in claim 4 wherein the input
means to the prosthesis comprises means for generating the audio
signals having frequencies within each of the pass bands of said
prosthesis, first selector means for selectively introducing each
of said audio signals to said prosthesis, and a variable
calibrating resistor coupled in series to said selector means.
9. Apparatus of the type described in claim 2 wherein said
measuring means further includes source means for introducing
complex phonic signals, a plurality of filter means coupled to said
source means for establishing discrete audio pass bands, said first
gain control means comprising independent gain controls coupled to
each of said filter means.
10. Apparatus of the type set forth in claim 9 wherein said
measuring means further includes summation means coupled to each of
said first gain control means, and a speaker coupled to said
summation means.
11. Apparatus of the type described in claim 2 wherein:
said measuring means further includes source means for introducing
complex phonic signals, a plurality of filter means coupled to said
source means for establishing discrete adjacent audio pass bands,
said first gain control means comprising independent gain controls
coupled to each of said filter means; and
the input means to the prosthesis comprises means for generating
audio signals having frequencies within each of the pass bands of
said prosthesis, first selector means for selectively introducing
each of said audio signals to said prosthesis, and a variable
calibrating resistor coupled in series to said selector means.
12. Apparatus of the type described in claim 2 wherein:
said measuring means further includes source means for introducing
complex phonic signals, a plurality of filter means coupled to said
source means for establishing discrete adjacent audio pass bands,
said first gain control means comprising independent gain controls
coupled to each of said filter means, summation means coupled to
each of said first gain control means, and a speaker coupled to
said summation means; and
the input means to the prosthesis comprises means for generating
audio signals having frequencies within each of the pass bands of
said prosthesis, first selector means for selectively introducing
each of said audio signals to said prosthesis, and a variable
calibrating resistor coupled in series to said selector means.
13. Apparatus of the type described in claim 1 wherein said first
and second gain control means each comprises an operational
amplifier having an input resistor and a shunt resistor, the
adjusting means of said first gain control means comprising a
variable input resistor, the adjusting means of said second gain
control means comprising a variable shunt resistor, each variable
input resistor being coupled to one of said variable shunt
resistors and simultaneously adjustable therewith.
14. Apparatus of the type described in claim 1 wherein said first
and second gain control means each comprises a variable attenuator,
the variable attenuator of each first gain control means being
coupled to an attenuator of said second gain control means such
that an increase in one attenuator causes a simultaneous decrease
in the other.
15. Apparatus for setting specific auditory deficiency corrections
in an arual prosthesis of the type having a plurality of filter
means providing audio pass bands and adjustable gain controls for
each pass band, the combination comprising:
input means for selectively introducing audio frequency signals to
said prosthesis, output means for receiving audio frequency signals
from said prosthesis, reciprocal gain control means electrically
coupled to said output means, said reciprocal gain control means
including means for adjusting the gain thereof, means calibrating
said gain adjusting means in units reciprocal to the gain of a
predetermined auditory deficiency correction, and means coupling
said reciprocal gain control to indicator means.
16. The method of setting a specific auditory deficiency correction
into an aural prosthesis of the type having at least one filter
means providing an audio pass band and an adjustable gain control
for said filter, the steps comprising:
measuring the gain required to provide a desired hearing
discrimination within said pass band, providing the reciprocal of
said measured gain and adjusting said gain control for said filter
so that the sum of the gain of said filter and reciprocal of said
measured gain in dB has a predetermined value.
17. The method of setting a specific auditory deficiency correction
into an aural prosthesis of the type having at least two filter
means each providing an audio pass band, the pass of one filter
being substantially completely included within the pass band of the
other filter and an adjustable gain control for said filters, the
steps including:
measuring the gain required to provide a desired hearing
discrimination within said pass bands;
providing the reciprocal of said measured gains; and
adjusting the gain control for said other filter so that the sum of
the gain of said other filter and the reciprocal of said measured
gain in dB has a predetermined value.
Description
BACKGROUND OF THE INVENTION
This invention relates to the sound amplification arts and to their
application in the amelioration of auditory deficiencies resulting
from damage to the sensori-neural structure of the human ear. It
relates particularly to apparatus for correcting deficiencies in a
person's ability to perceive and to comprehend spoken language.
Sensori-neural hearing loss is generally considered to be the most
prevalent type of auditory handicap found in the United States as
well as in other civilized cultures. It constitutes a significant
barrier to adequate communication in 5% to 10% of the total United
States population and in more than 50% of the population over 60
years of age. Furthermore, these proportions are expected to
increase in conjunction with ongoing increases in ambient noise
levels and life expectancy in our society.
Sensori-neural impairment may result from any one or more of a
number of causes including, but not limited to, genetic and
congenital factors, viral diseases, specific toxic agents,
circulatory disturbances, specific physical trauma and excessive
exposure to noise. Irrespective of the primary cause, however,
sensory cells within the organ of hearing or their associated
neural units suffer some degree of damage and are rendered
partially or totally incapable of fulfilling their respective roles
in the processing of auditory information. This form of damage
cannot be repaired by means of currently known medical or surgical
techniques, and the probability of discovery of effective
techniques, within the forseeable future appears rather remote.
Thus, in virtually all cases of sensori-neural hearing loss,
amplification of incoming sounds represents the only possible means
for restoring adequate hearing ability.
Hearing loss resulting from sensori-neural damage is usually
irregular with respect to frequency, being selectively greater for
particular portions of the audible frequency range. The ability to
hear sounds in the range above 1000 Hz is often affected more than
the hearing of sounds below 1000 Hz, although this is by no means a
universal observation. The ultimate consequency of irregular
hearing acuity for various portions of the audio frequency spectrum
is distortion in the perception of complex sounds, i.e., sounds
composed of a number of different frequencies.
A certain amount of distortion in complex sounds may be tolerable,
but current information does not permit precise specification of
the maximum amount of each type of distortion which may exist
without interfering materially with accurate sound recognition.
Many gross sounds, for example, do not demand a great deal of
analytic power in the auditory system, so even a rather severely
impaired system may function adequately in the interpretation of
such sounds.
In audiologic parlance, the term "discrimination" denotes the
capacity of the ear to analyze incoming acoustic patterns and
interpret them appropriately. Analytic power may fail at any of
several stages in the auditory process, commonly in the organ of
hearing or first order neurons due to damage to these structures.
Since the ear may be required to perform many degrees of
discrimination, varying from extremely coarse to extremely fine,
its analytic power may be measured through the use of tests which
demand auditory discriminations of progressive difficulty until
failure occurs.
Among the most difficult discriminations required of the human ear
are those necessary for accurate interpretation of speech,
particularly speech in the presence of noise. Tests of speech
discrimination are commonly employed, therefore, to derive a
realistic estimate of a person's everyday functional adequacy in
hearing.
Each of the phonic units of a spoken word is a complex sound,
composed of several frequencies clustered in a more-or-less
definable range. When the acuity of the ear has been selectively
impaired in a specific frequency range, speech sounds or their
components falling in that range may be heard at a reduced
intensity or not at all. Impairment in several frequency ranges
compounds the difficulty and is probably responsible in large
measure for the primary complaint of the individual with
sensori-neural hearing loss that he can hear a speaker's voice but
cannot understand what is said. The mechanism for inhibiting such
understanding may be the nonlinear responses that result in
intermodulation products and harmonics which could cause
interference with the desired spectral components of speech.
On the basis of the foregoing information, it would seem quite
reasonable to deal with sensori-neural hearing loss by selective
spectrum amplification; that is, providing amplification only in
those frequency ranges or bands in which acuity is deficient, and
only in the amount of the deficiency. Thus, the ultimate value of
selective spectrum amplification rests on the application of
appropriate methods for measuring the degree of auditory deficiency
as a function of various frequency bands, and also on the
construction of a wearable device which is fully capable of
producing amplification to compensate for the measured
deficiencies. Because of existing inadequacies in both respects,
the principle of selective amplification has fallen into disrepute,
for the hearing aid industry has adopted the pure tone (single
frequency) threshold audiogram as the criterion measurement and has
produced hearing aids with inadequate capabilities for providing
proper acoustic output at each portion of the audio band.
The threshold audiogram curve represents an individual's measured
absolute auditory threshold for a series of pure frequency tones,
usually in the range of 250 Hz to 8000 Hz sampled at octave
intervals on the assumption that intra-octave tone thresholds
follow the general audiogram contour. However, it is demonstrable
that fairly marked departures from this overall pattern may exist
at intermediate frequencies, i.e., frequencies between pure tones
one octave apart. In fact, careful consideration of the types of
measurements which are genuinely helpful in guiding the design of
particular hearing aid features suggests that the pure tone
threshold curve is virtually useless for several reasons:
A. under everyday circumstances, individuals react only to
supra-threshold sounds, as these are sounds of primary
significance. For practical purposes, threshold sounds remain
unnoticed.
B. the contour of an individual's threshold curve is observably
different from the contour of his supra-threshold equal loudness
curves or comfortable listening level curves.
C. an individual's recognition of complex phonic units or their
combination into spoken words is essentially unrelated to his
acuity for individual pure tones.
Control of acoustic output in current hearing aids is ordinarily
achieved through manipulation of frequency response, which refers
to the acoustic output of a sound transmission system at each of
the frequencies within its pass band when the input level is
maintained constant for all frequencies. A graphic representation
of a system's frequency response is referred to as a response
characteristic, curve or contour. Manufacturers commonly claim that
they are able to build hearing aids to yield any required frequency
response; but this does not appear to be the case in practice
because there are definite limitations on the band widths and
response curves available in present day aids. In practice,
manufacturers use combinations of components which produce a
limited choice of response patterns and simply select one which
most closely corresponds to the criterion, which, as mentioned
earlier, usually is a threshold audiogram curve.
One additional comment is relevant as a preface to the innovative
concepts to which the present invention is particularly addressed.
It is generally recognized that the ear with sensori-neural hearing
loss is excessively susceptible to overloading, which is to say
that, although it may be relatively insensitive to sounds of low or
moderate intensity, it is hypersensitive to sounds of higher
intensity (i.e., nonlinear response characteristics). This
condition restricts the useful operating range of the ear, referred
to as the dynamic range; that is, the decibel difference between
the lowest intensity at which a sound is reliably detected
(absolute threshold) and the upper limit of comfortable loudness
for that sound (discomfort threshold).
Whereas, the dynamic range of the normal ear is of the order of 100
dB, the range of a sensori-neurally impaired ear may be as little
as 10 or 15 DB, generally over a limited frequency spectrum range.
Thus, for an impaired ear to function with any degree of adequacy,
the full intensity range of thet outside acoustic world must be
restricted in some way to fit through an abnormally small sound
window and such restriction must cause minimal intermodulation
products, harmonics, and so forth which would result in distortion.
Without such restriction, the ear is readily overloaded, leading to
psychologic or physical annoyance and distortion of incoming
acoustic patterns.
The consequences of overloading have been appreciated for many
years, and output compression devices are widely used in today's
hearing aids. Without exception, however, these devices operate on
a broad frequency band, so that when any frequency component of a
signal reaches a predetermined critical level, the entire pass band
of the hearing aid is compressed. Consequently, the components
which are not at a critical intensity are needlessly
attenuated.
Our evaluation of relevant factors have led to the evolution of
several innovative concepts providing improved methods and
apparatus for measuring and defining auditory deficiencies in terms
of a prescription for compenstory amplification, but then the
remaining difficulty is the proper adjustment of the prosthetic
device itself in order to assure that the prescribed compensatory
amplification spectrum is operatively provided in the prosthetic
device.
Modern wearable hearing aids vary considerably in circuitry and in
the degree to which adjustments can be made in operating
characteristics. Some have volume controls, maximum power output
controls, some have no filter, others may have one or more filters,
which provide frequency bands which may or may not be adjacent. In
fact, in some hearing aids having multiple filters, one filter may
provide a band which is completely or almost completely within the
band of another filter. Even though gain controls may be provided
for specific frequency bands, such devices are difficult to
properly calibrate, particularly those aids worn entirely in or
about the ear, they being quite small. Generally, no calibration
indicia are provided for such devices, the adjusting screws are
very small and are usually located inside a cover which must be
removed in order to obtain access thereto. Adjusting a hearing aid
while it is fitted to the patient's ear is considered a very
unsatisfactory procedure as the very act of adjusting the tiny
screws creates noises which are annoying to the patient. In
addition to those problems, it is highly desirable to use unskilled
or semiskilled labor for fitting hearing aids, and therefore a
sufficiently simple and foolproof method and apparatus for
incorporating the hearing profile prescription into the aid would
be of considerable value.
SUMMARY OF THE INVENTION
It is a particular object of the present invention to provide
apparatus such that hearing aids capable of compensatory amplitude
and frequency adjustments can be fitted to a prescribed hearing
curve by unskilled or semiskilled persons, specifically those
engaged in the actual dispensing of such devices.
It is also an object of the present invention to provide simplified
apparatus such that a patient's hearing curve can be ascertained by
testing his hearing response for mixed inputs of speech and noise,
obtaining preferred discrimination levels for each of the bands
utilized, and then providing a means for selecting and matching the
hearing aid itself to those tested levels without the necessity for
complex electronic testing or measuring devices.
The foregoing objects of the present invention are realized by
providing a testing apparatus in which the input signal is first
divided into a plurality of frequency bands and then the gain is
adjusted until the person undergoing the test indicates a preferred
discrimination condition. The gain is adjusted by use of large
controls by which fine adjustments can easily be made. As the gain
is adjusted for each of the frequency bands, the adjusting
mechanism provides a reciprocal gain adjustment which is set at the
same time into the testing apparatus. Thereafter, an adjustable
hearing aid device or prosthesis which is considered proper for the
person is coupled to the reciprocal gain adjustment mechanism of
the testing apparatus. The hearing aid includes an amplifier and
may or may not include one or more filters, and it may or may not
include a maximum power output device. The control for the maximum
power output, the gain control of the amplifier and the gain
control of the filters, if used, are adjusted until an equality is
indicated on the testing apparatus whereby the hearing device is
thereupon matched to the patient's tested hearing curve. It will be
particularly noticed that, according to this invention, no reading
is taken from the testing apparatus and remembered, or written down
and then transferred manually to the prosthesis. On the contrary,
the readings are stored mechanically or electrically by the setting
of the reciprocal gain adjustments in the testing apparatus and the
transfer of the test results from the testing apparatus to the
prosthesis is electrical rather than manual.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustrating an exemplary embodiment of
the basic concepts of the present invention in which a master
hearing aid is provided for initially determining the patient's
hearing curve.
FIG. 2 is a block diagram of an alternate embodiment of the present
invention utilizing analogous but somewhat distinct features.
FIG. 3 is a block diagram demonstrating the manner in which a
wearable hearing aid is coupled to the testing apparatus for
adjustment of the wearable aid to match the curve determined by the
master hearing aid.
FIG. 4 is a partial circuit diagram of alternative embodiment of
the present invention providing another means for setting the gain
of the hearing aid to the reciprocal of the gain ascertained by the
master hearing aid.
DESCRIPTION OF A PREFERRED EMBODIMENT
FIG. 1 represents schematically a master hearing aid device for
empirically determining a person's hearing characteristics. A
speaker 10 is inserted in the patient's ear and a mixture of speech
and background noise is generated from source 12. As previously
mentioned herein and as more specifically set forth in the
previously issued patents referenced herein, the most useful
hearing profile for a patient is determined by obtaining his
discrimination responses to a mixture of spoken words heard in
conjunction with background noise as this most accurately simulates
the normal listening situation. The output from source 12 is then
sent through a plurality of filters 14, 16 and 18. Filter 18 is
designated filter "N" representing that the number of filters is
not necessarily three, as shown in the drawings for the purposes of
convenience of explanation, but in fact the number of filters can
be more or less than three covering the audible frequency spectrum
commencing from about 250 Hz to 8000 Hz in octave intervals.
The volume of sound passing through band pass filter 14 is
controlled by gain control circuit generally designated 20 which
includes an operational amplifier 22, a variable input resistor 24
and a fixed shunt resistor 26. As resistance 24 is increased, the
overall gain of unit 20 is decreased, and vice versa. A reciprocal
gain control unit 30 is associated with gain control unit 20 and
consists of an operational amplifier 32 substantially similar in
configuration to operational amplifier 22, except that amplifier 32
has a fixed input resistor 34 and a variable shunt resistor 36.
Variable resistors 24 and 36 are mechanically coupled onto the same
control shaft so that gain controls 20 and 30 are reciprocal and
the sum of the gains in decibels is always the same. This is
accomplished in that as resistor 24 is increased, for example,
resistor 36 is so mounted that it is also increased. As the input
resistor to amplifier 22 is increased, the gain decreases and, as
the shunt resistor 36 is increased, the gain for amplifier 32
increases by the same amount.
At the initial testing stage of the master hearing aid unit,
amplifier 32 is not in fact operational, but the shunt resistance
is being adjusted in unison with the adjustment of the input
resistor to amplifier 22. The gain control, therefore, of unit 20
is manipulated in the well-known manner until the patient indicates
a preferred level of word discrimination. The output of filters 16
and 18 are likewise fed to similar gain control units 38 and 40,
each of which is similarly coupled to a reciprocal gain control
unit in the same manner as previously described, although these are
not shown in the drawing. Suffice it to say that in each case, as
the gain control units 20, 38 and 40 are adjusted, the reciprocal
of the gain of each of those units is stored on each of the
variable input resistors and, therefore, the reciprocal gain
control units are thereby adjusted for future use. Each of the
outputs from the gain control units 20, 38 and 40 is fed to a
summer 42, the output of which supplies the speaker 10. Instead of
feeding the input speech and noise from the source 12
simultaneously to all filter units, one can by appropriate
switching feed the input sound to each of the filters
separately.
For the maximum power output test, a gain control unit such as 41
may be used without a filter in its input. Desired maximum power in
each filter pass band and/or overall maximum power may be
determined by a suitable means, leaving the desired settings on the
appropriate controls, similar to the gain settings.
FIG. 2 shows an alternative system closely resembling that shown in
FIG. 1, except that in place of operational amplifiers, the gains
are varied using attenuators. In FIG. 2, the output from filter 14
is passed to amplifier 44, the output of which is fed through a
variable series resistor 46, the output of which then goes to the
summer 42. The variable resistor 46 is similarly mechanically
coupled to another resistor 48 as by being mounted upon the same
control shaft, such that as resistor 46 is increased or decreased,
resistor 48 is decreased or increased.
Turning now to FIG. 3, a system is shown for the setting of a
wearable hearing aid in accordance with the audiological curve now
set into the instrument as described with respect to FIG. 1. In
FIG. 3, the system consists of a plurality of single frequency
sources 50, 51 and 52 providing output signals of equal amplitude
and having the frequencies of the filters 14, 16 and 18. Again, the
number of sources 50-52 corresponds to the number of filters
provided in the master hearing aid, as would be readily apparent,
or a single variable source may be used. A selector switch 54
selects the output of one of the sources and, according to the
method of the present invention, the dispensing audiologist selects
that source having a frequency to which the person being fitted is
least sensitive, in other words, the frequency at which the most
gain is needed. The output of the selected frequency source is then
applied through a calibrating resistor 56 and an amplifier 58, if
necessary, to the input of the wearable hearing aid 60 to be
adjusted. In this hearing aid, there are a number of adjustable
elements, including a master volume control and individual gain
controls for each pass band in that aid and possibly individual
power output controls for each pass band and/or an overall power
output control.
The hearing aid or prosthesis 60 is chosen by the dispensing
audiologist to improve the hearing of the person as indicated to
the audiologist by hearing tests and may include an amplifier but
no filter or one or more filters which may or may not provide
adjacent bands. In fact, in one type of hearing aid, a filter may
provide a band pass that is wholly or nearly wholly within the pass
band of another filter and either the wide or the narrow or both
filters may be adjusted in this specification. The term "filter"
includes any apparatus which alters the frequency response of the
audio wave applied thereto. Also, as will be further explained, the
prosthesis may contain power output controls 63, 67, 65 and the
control 81 therefor.
The volume control 62 is first adjusted to maximum gain and all
power output controls, such as 81, are set to maximum power output.
The output of the hearing aid is then coupled to the inputs of the
reciprocal gain control units, such as unit 30, and the same is
true with respect to the other reciprocal gain control units as
previously described in conjunction with FIG. 1. A selector switch
64 is coupled to the outputs of the reciprocal gain control units
and to an indicator 66. In this configuration, with switch 64
selected to receive the output from the gain control unit
corresponding to the frequency source previously selected by switch
54, then the corresponding filter 68, that is, the filter having
the pass band corresponding to the selected source and the selected
reciprocal gain control unit, is adjusted by means of an adjusting
screw 70 to maximum gain and then the calibrating resistor 56 is
adjusted until the indicator 66 reads a predetermined reference
level. If measured in decibels (dB), the sum of the gain of the
unit 30 and that provided by setting the screw 70 should have a
predetermined value. The indicator 66 may be a meter or a blinking
light or any device that indicates when a certain amplitude level
is reached. This initial calibration having been accomplished,
calibrating resistor 56 will not be changed again while setting the
gains of the other filters of the wearable hearing aid 60.
Switch 54 is next turned to another frequency source, such as 51,
and switch 64 is turned to the corresponding reciprocal gain
control unit. Then, gain control 72 for filter 73 is adjusted until
the indicator 66 reads the same as it did with the previous source.
Again, switch 54 is turned to another frequency source, such as 52,
selector switch 64 is again switched to the corresponding
reciprocal gain control unit and then gain control unit 74 for
filter 75 is adjusted until the indicator 66 again reads the same
level. This sequence is repeated for each filter source. In this
manner, hearing aid 60 is adjusted in accordance with the
audiological profile prescribed by use of the master hearing aid of
FIG. 1.
The maximum power output feature of the hearing aid 60 includes the
elements 61, 63, 65 and 67. It will be noted that of these
elements, elements 61, 63 and 67 comprise a known automatic gain
control device, to which is added the variable resistor 65 in the
feedback path of the automatic gain control device. This resistor
65 is varied by varying control 81.
To set the maximum power output, switch 54 is set to frequency
source 53, which has an amplitude and frequency which will activate
the power output mechanism associated with control 81. Control 81
is adjusted until indicator 66 shows that the desired level stored
in unit 41 is reached. This process may be repeated for each power
output control in the wearable hearing aid, if more than one is
provided, with appropriate changes in the frequency of source
53.
It will be apparent that instead of using the system employing
operational amplifiers, as set forth in FIG. 1, and the reciprocal
amplifiers, as shown in FIG. 3, the reciprocal resistors 48 and
amplifiers 44, as shown in FIG. 2, may be used in the same manner
for adjustment of the pass band gains and the power output of the
hearing aid.
As another variation of the present invention, a reciprocal
operational amplifier 80, as shown in FIG. 4, may be provided as a
separate piece of equipment not associated with the gain control
units 20, 38 and 40 of the master hearing aid. The operational
amplifier 80 is of similar configuration to those shown in FIG. 1,
including an amplifier 82, input resistor 84 and a variable shunt
resistor 86. The control shaft of variable resistor 86 is coupled
to a reciprocally calibrated dial 88. The single operational
amplifier 80 can then be used in a manner similar to that described
with respect to FIG. 3, except that the single amplifier is used
for setting the gain control of each of the frequency bands in the
hearing aid 60. This is accomplished by taking the calibrated
reading from the setting of resistor 24, for example, and by
setting the reciprocally calibrated dial 88 to the same value,
resistor 86 to automatically set so that amplifier 80 provides a
gain which is the reciprocal of the gain of gain control unit 20.
The same procedure can be followed for each of the gain control
units by different settings of the reciprocal dial 88 for adjusting
all of the frequency bands of hearing aid 60.
While particular embodiments of the present invention have been
shown and described herein, such embodiments are to be considered
in all respects as illustrative and not restrictive, and it will be
apparent to those skilled in the art that many modifications,
changes and alterations might be made within the scope of the
invention without departing from its inventive concepts, and all
changes which come with the meaning and range of equivalence of the
claims therefore are intended to be embraced therein.
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